The "Route MIDI Input to: " checkbox is an additional, optional layer of MIDI routing between the host (or your controller, in standalone mode) and BPM. 

• When the box is unchecked, BPM receives MIDI input just like any other VI. Use MIDI tracks in the host assigned the desired channel (or in standalone, change the transmit channel on your controller). 
• When the box is checked, MIDI input will be routed to the item in the drop-down menu to the right of the "Route MIDI Input to: " label. In this way, you could use a single MIDI track in your host assigned to any BPM MIDI input (or in standalone, transmit on any channel from your controller), and the MIDI input will be routed to the chosen destination, be it "Selected Bank/Part" or a particular port & channel. 

Whether this option is checked or not, you still need at least one MIDI input properly designated from the host.